/*
* lz_sarray.h
*
- * Suffix array match-finder for LZ (Lempel-Ziv) compression.
+ * Suffix array match-finder for Lempel-Ziv compression.
*/
/*
#ifndef _WIMLIB_LZ_SARRAY_H
#define _WIMLIB_LZ_SARRAY_H
-#include "wimlib/compiler.h"
-#include "wimlib/lz.h"
-#include "wimlib/types.h"
+#include "wimlib/compiler.h" /* must define '_always_inline_attribute' */
+#include "wimlib/lz.h" /* must define 'struct raw_match', 'input_idx_t',
+ and LZ_ASSERT(). */
+#include "wimlib/types.h" /* must define 'bool', 'u8', 'u32' */
struct salink;
-/* Suffix array LZ (Lempel-Ziv) match-finder. */
+/* State of the suffix array LZ (Lempel-Ziv) match-finder.
+ *
+ * This is defined here for benefit of the inlined code. It's not intended for
+ * code outside the match-finder itself to read or write members from this
+ * structure. */
struct lz_sarray {
- /* Allocated window size for the match-finder. */
+ /* Allocated window size for the match-finder.
+ *
+ * Note: this match-finder does not store the window itself, as the
+ * suffix array (@SA) and associated arrays (@ISA, @LCP, @salink) are
+ * sufficient to find matches. This number is the maximum length of
+ * those arrays, or also the maximum window (block) size that can be
+ * passed to lz_sarray_load_window(). */
input_idx_t max_window_size;
/* Minimum match length to return. */
/* Maximum number of matches to return at each position. */
u32 max_matches_to_return;
- /* Current position in the window */
+ /* Current position in the window. */
input_idx_t cur_pos;
/* Current window size. */
input_idx_t window_size;
- /* Suffix array for window.
+ /* Suffix array for the current window.
* This is a mapping from suffix rank to suffix position. */
input_idx_t *SA;
- /* Inverse suffix array for window.
+ /* Inverse suffix array for the current window.
* This is a mapping from suffix position to suffix rank.
* If 0 <= r < window_size, then ISA[SA[r]] == r. */
input_idx_t *ISA;
- /* Longest common prefix array corresponding to the suffix array SA.
- * LCP[i] is the length of the longest common prefix between the
- * suffixes with positions SA[i - 1] and SA[i]. LCP[0] is undefined.
- */
- input_idx_t *LCP;
-
/* Suffix array links.
*
* During a linear scan of the input string to find matches, this array
struct salink *salink;
};
-/* Suffix array link */
+/* Suffix array link; one of these exists for each position in the suffix array.
+ */
struct salink {
/* Rank of highest ranked suffix that has rank lower than the suffix
* corresponding to this structure and either has a lower position
* (initially) or has a position lower than the highest position at
- * which matches have been searched for so far, or -1 if there is no
- * such suffix. */
+ * which matches have been searched for so far, or ~(input_idx_t)0 if
+ * there is no such suffix.
+ *
+ * Think of this as a pointer to the closest position in the suffix
+ * array to the left that corresponds to a suffix that begins at a
+ * position in the current dictionary (i.e. before the current position
+ * in the window). */
input_idx_t prev;
/* Rank of lowest ranked suffix that has rank greater than the suffix
* corresponding to this structure and either has a lower position
* (intially) or has a position lower than the highest position at which
- * matches have been searched for so far, or -1 if there is no such
- * suffix. */
+ * matches have been searched for so far, or ~(input_idx_t)0 if there is
+ * no such suffix.
+
+ * Think of this as a pointer to the closest position in the suffix
+ * array to the right that corresponds to a suffix that begins at a
+ * position in the current dictionary (i.e. before the current position
+ * in the window). */
input_idx_t next;
/* Length of longest common prefix between the suffix corresponding to
- * this structure and the suffix with rank @prev, or 0 if @prev is -1.
- */
+ * this structure and the suffix with rank @prev, or 0 if @prev is
+ * ~(input_idx_t)0. */
input_idx_t lcpprev;
/* Length of longest common prefix between the suffix corresponding to
- * this structure and the suffix with rank @next, or 0 if @next is -1.
- */
+ * this structure and the suffix with rank @next, or 0 if @next is
+ * ~(input_idx_t)0. */
input_idx_t lcpnext;
};
+/*-----------------------------------*/
+/* Functions defined in lz_sarray.c */
+/*-----------------------------------*/
+
extern bool
lz_sarray_init(struct lz_sarray *mf,
- input_idx_t max_window_size,
- input_idx_t min_match_len,
- input_idx_t max_match_len,
- u32 max_matches_to_consider,
- u32 max_matches_to_return);
+ input_idx_t max_window_size,
+ input_idx_t min_match_len,
+ input_idx_t max_match_len,
+ u32 max_matches_to_consider,
+ u32 max_matches_to_return);
extern void
lz_sarray_destroy(struct lz_sarray *mf);
extern void
-lz_sarray_load_window(struct lz_sarray *mf, const u8 window[],
- input_idx_t window_size);
+lz_sarray_load_window(struct lz_sarray *mf, const u8 T[], input_idx_t n);
-static inline input_idx_t
+/*-------------------*/
+/* Inline functions */
+/*-------------------*/
+
+static _always_inline_attribute input_idx_t
lz_sarray_get_pos(const struct lz_sarray *mf)
{
return mf->cur_pos;
const input_idx_t r = ISA[i];
/* next = rank of LOWEST ranked suffix that is ranked HIGHER than the
- * current suffix AND has a LOWER position, or -1 if none exists. */
+ * current suffix AND has a LOWER position, or ~(input_idx_t)0 if none
+ * exists. */
const input_idx_t next = link[r].next;
/* prev = rank of HIGHEST ranked suffix that is ranked LOWER than the
- * current suffix AND has a LOWER position, or -1 if none exists. */
+ * current suffix AND has a LOWER position, or ~(input_idx_t)0 if none
+ * exists. */
const input_idx_t prev = link[r].prev;
/* Link the suffix at the current position into the linked list that
- * contains all suffixes in the suffix array that are appear at or
- * before the current position, sorted by rank.
- *
- * Save the values of all fields we overwrite so that rollback is
- * possible. */
+ * contains all suffixes referenced by the suffix array that appear at
+ * or before the current position, sorted by rank. */
if (next != ~(input_idx_t)0) {
-
link[next].prev = r;
link[next].lcpprev = link[r].lcpnext;
}
if (prev != ~(input_idx_t)0) {
-
link[prev].next = r;
link[prev].lcpnext = link[r].lcpprev;
}
#define LZ_SARRAY_INFINITE_COST (~(lz_sarray_cost_t)0)
/*
- * Use the suffix array match-finder to retrieve a list of LZ matches at the
+ * Use the suffix array match-finder to retrieve a list of matches at the
* current position.
*
* Returns the number of matches written into @matches. The matches are
* returned in decreasing order by length, and each will be of unique length
- * between the minimum and maximum match lengths passed to lz_sarray_init(). Up
- * to @max_matches_to_return (passed to lz_sarray_init()) matches will be
- * returned.
+ * between the minimum and maximum match lengths (inclusively) passed to
+ * lz_sarray_init(). Up to @max_matches_to_return (passed to lz_sarray_init())
+ * matches will be returned.
*
* @eval_match_cost is a function for evaluating the cost of a match when
- * deciding which ones to return. It is only used for comparing matches of the
- * same length. It needs to be fast, and need not be exact; an implementation
- * might simply rank matches by their offset, for example, although
- * implementations may choose to take into account additional information such
- * as repeat offsets.
+ * deciding which ones to return. It needs to be fast, and need not be exact;
+ * an implementation might simply rank matches by their offset, for example,
+ * although implementations may choose to take into account additional
+ * information such as repeat offsets.
*/
static _always_inline_attribute u32
lz_sarray_get_matches(struct lz_sarray *mf,
/* best_cost = cost of lowest-cost match found so far.
*
* We keep track of this so that we can ignore shorter matches that do
- * not have lower costs than a longer matches already found.
- */
+ * not have lower costs than longer matches already found. */
lz_sarray_cost_t best_cost = LZ_SARRAY_INFINITE_COST;
/* count_remaining = maximum number of possible matches remaining to be
git://wimlib.net / wimlib / blobdiff